Evaluation of a calibration constant of a narrow-band solar UV-B radiometer

Since 1990, global solar UV-B irradiance has been measured by a narrow-band solar UV-B radiometer at Hiratsuka, Japan. To detect long-term trend of global solar UV-B irradiance measured by the narrow-band solar UV-B radiometer, evaluation of a calibration constant of the radiometer for accurate measurement is essential. Thus, for estimating trend of global solar UV-B irradiance from 2000 to 2003, the calibration constant of the narrow-band solar UV-B radiometer was evaluated by applying three methods. The first method is based on a spectral irradiance standard lamp, which has been applied when evaluating long-term trend of global solar UV-B irradiance from October 1990 to September 2000. The second one is based on a reference narrow-band solar UV-B radiometer. Global solar UV-B irradiance measured by our narrow-band solar UV-B radiometer was compared with that of the reference narrow-band solar UV-B radiometer under natural sunlight. The third one is based on the total ozone amount. The results with three methods showed good agreement within 5%, leading to the conclusion that three methods are comparable in evaluating the calibration constant of the narrow-band solar UV-B radiometer.